I love my SKS it goes bang every trigger pull and its quick to load and easy to use. My SVT 40 not so much, it doesn't go bang everytime (depends on the ammo your using), its a bit more difficult to load (I use stripper clips and the 7.62x54r ones are not nearly as good as the 7.62x39 ones), and its more difficult to use (gas settings, more difficult teardown etc.). But if you don't have a SVT 40 and you do have a SKS I would go for the SVT.
Another idea is if your looking for a high quality semi-auto in the same price range and production range as the SVT 40 (maybe a 100 or 200 above depending) I would suggest looking at a AG-42b. There maybe no surplus around for it anymore but it is a cool semi-auto which is reliable and easy to maintain once you get the hang of how it works.